Impact of bone marrow-derived signals on NK cell development and functional maturation

Characterization of anti-asialo-GM1 monoclonal antibody

Asialo-GM1 (ASGM1) has been identified as a cell surface marker of murine NK cells. Although polyclonal anti-asialo-GM1 antibodies (anti-ASGM1 pAb) have been widely used for studying natural killer (NK) cell functions in vivo, the technical challenges have existed in their specificity for NK cell depletion. Furthermore, the exact expression of ASGM1 on the NK cell lineage and other immune cells has not been characterized due to the lack of appropriate reagents. In this context, we have recently established several clones of monoclonal antibodies against ASGM1 with different specificity to other structurally related gangliosides. In this study, we characterized the rabbit anti-ASGM1 mAb clone GA134 with both higher specificity to ASGM1 and efficacy in depleting NK cells, and the in vivo GA134 treatment significantly impaired NK cell-dependent anti-tumor effector function. We further determined the expression of ASGM1 on the NK cell lineage at distinct differentiation stages using fluorescent-labeled GA134 and found that both CD122+ NK1.1- NKP and immature NK1.1+ CD11blo CD27lo NK subsets were the earliest NK cell lineages acquiring ASGM1 expression on their cell surface. In addition to NK cells, we characterized the expression of ASGM1 on a subpopulation of T cells, mostly NK1.1+ T cells, and basophils.

Strong capacity of differentiated PD-L1 CAR-modified UCB-CD34+ cells and PD-L1 CAR-modified UCB-CD34+-derived NK cells in killing target cells and restoration of the anti-tumor function of PD-1-high exhausted T Cells

BACKGROUND

Using natural killer (NK) cells to treat hematopoietic and solid tumors has great promise. Despite their availability from peripheral blood and cord blood, stem cell-derived NK cells provide an "off-the-shelf" solution.

METHODS

In this study, we developed two CAR-NK cells targeting PD-L1 derived from lentiviral transduction of human umbilical cord blood (UCB)-CD34+ cells and UCB-CD34+-derived NK cells. The transduction efficiencies and in vitro cytotoxic functions including degranulation, cytokine production, and cancer cell necrosis of both resultants PD-L1 CAR-NK cells were tested in vitro on two different PD-L1 low and high-expressing solid tumor cell lines.

RESULTS

Differentiated CAR‑modified UCB-CD34+ cells exhibited enhanced transduction efficiency. The expression of anti-PD-L1 CAR significantly (P < 0.05) enhanced the cytotoxicity of differentiated CAR‑modified UCB-CD34+ cells and CAR-modified UCB-CD34+-derived NK cells against PD-L1 high-expressing tumor cell line. In addition, CAR-modified UCB-CD34+-derived NK cells significantly (P < 0.05) restored the tumor-killing ability of exhausted PD-1 high T cells.

CONCLUSION

Considering the more efficient transduction in stem cells and the possibility of producing CAR-NK cell products with higher yields, this approach is recommended for studies in the field of CAR-NK cells. Also, a pre-clinical study is now necessary to evaluate the safety and efficacy of these two CAR-NK cells individually and in combination with other therapeutic approaches.

Current status and future perspective of natural killer cell therapy for cancer

Natural killer (NK) cells possess innate abilities to effectively eliminate cancer cells. However, because of difficulties of proliferation and easy to be induced dysfunction in the setting of cancer post NK cell therapy, the curative effect of NK cell infusion has been constrained and not been widely applicable in clinical practice. The rapid development of biotechnology has promoted the development of NK cell therapy for cancer treatment. In this review, we will provide a comprehensive analysis of the current status and future prospects of NK cell therapy for cancer, focusing on the biological characteristics of NK cells, as well as strategies to enhance their targeting capabilities and overcome tumor immune suppression within the microenvironment.

Role of Natural Killer Cells during Pregnancy and Related Complications

A high number of leucocytes reside in the human endometrium and are distributed differentially during the menstrual cycle and pregnancy. During early pregnancy, decidual natural killer (dNK) cells are the most common type of natural killer (NK) cells in the uterus. The increase in the number of uterine NK (uNK) cells during the mid-secretory phase of the menstrual cycle, followed by further increase of dNK cells in early pregnancy, has heightened interest in their involvement during pregnancy. Extensive research has revealed various roles of dNK cells during pregnancy including the formation of new blood vessels, migration of trophoblasts, and immunological tolerance. The present review article is focused on the significance of NK cells during pregnancy and their role in pregnancy-related diseases. The article will provide an in-depth review of cellular and molecular interactions during pregnancy and related disorders, with NK cells playing a pivotal role. Moreover, this study will help researchers to understand the physiology of normal pregnancy and related complications with respect to NK cells, so that future research work can be designed to alleviate the complications.

NF-κB c-Rel Is Dispensable for the Development but Is Required for the Cytotoxic Function of NK Cells

Natural Killer (NK) cells are cytotoxic lymphocytes critical to the innate immune system. We found that germline deficiency of NF-κB c-Rel results in a marked decrease in cytotoxic function of NK cells, both in vitro and in vivo, with no significant differences in the stages of NK cell development. We found that c-Rel binds to the promoters of perforin and granzyme B, two key proteins required for NK cytotoxicity, and controls their expression. We generated a NK cell specific c-Rel conditional knockout to study NK cell intrinsic role of c- Rel and found that both global and conditional c-Rel deficiency leads to decreased perforin and granzyme B expression and thereby cytotoxic function. We also confirmed the role of c-Rel in perforin and granzyme B expression in human NK cells. c-Rel reconstitution rescued perforin and granzyme B expressions in c-Rel deficient NK cells and restored their cytotoxic function. Our results show a previously unknown role of c-Rel in transcriptional regulation of perforin and granzyme B expressions and control of NK cell cytotoxic function.

Transcription Factors Associated With IL-15 Cytokine Signaling During NK Cell Development

Natural killer (NK) cells are lymphocytes primarily involved in innate immunity and possess important functional properties in anti-viral and anti-tumor responses; thus, these cells have broad potential for clinical utilization. NK cells originate from hematopoietic stem cells (HSCs) through the following two independent and continuous processes: early commitment from HSCs to IL-15-responsive NK cell progenitors (NKPs) and subsequent differentiation into mature NK cells in response to IL-15. IL-15 is the most important cytokine for NK cell development, is produced by both hematopoietic and nonhematopoietic cells, and functions through a distinct delivery process termed transpresentation. Upon being transpresented to NK cells, IL-15 contributes to NK cell development via the activation of several downstream signaling pathways, including the Ras-MEK-MAPK, JAK-STAT5, and PI3K-ATK-mTOR pathways. Nonetheless, the exact role of IL-15 in NK cell development has not been discussed in a consecutive and comprehensive manner. Here, we review current knowledge about the indispensable role of IL-15 in NK cell development and address which cells produce IL-15 to support NK cell development and when IL-15 exerts its function during multiple developmental stages. Specifically, we highlight how IL-15 supports NK cell development by elucidating the distinct transpresentation of IL-15 to NK cells and revealing the downstream target of IL-15 signaling during NK cell development.

Increased Expression of TIGIT/CD57 in Peripheral Blood/Bone Marrow NK Cells in Patients with Chronic Myeloid Leukemia

The antitumor activity of NK cells in patients with chronic myeloid leukemia (CML) is inhibited by the leukemia microenvironment. Recent studies have identified that the expression of TIGIT, CD57, and KLRG1 is related to the function, maturation, and antitumor capabilities of NK cells. However, the characteristics of the expression of these genes in the peripheral blood (PB) and bone marrow (BM) from patients with CML remain unknown. In this study, we used multicolor flow cytometry to assay the quantity and phenotypic changes of NK cells in PB and BM from de novo CML (DN-CML) and CML patients acquiring molecular response (MR-CML). We found that the expression of TIGIT, which inhibits NK cell function, is increased on CD56⁺ and CD56^dim NK cells in DN-CML PB compared with those in healthy individuals (HIs), and it is restored to normal in patients who achieve MR. We also found that the expression of CD57 on NK cells was approximately the same level in PB and BM from DN-CML patients, while decreased CD57 expression was found on CD56⁺ and CD56^dim NK cells in HI BM compared with PB. Additionally, those two subsets were significantly increased in DN-CML BM compared to HI BM. The expression of CD57 correlates with replicative senescence and maturity for human NK cells; therefore, the increase in TIGIT on PB NK cells together with an increase in CD57 on BM NK cells may explain the subdued NK cell antileukemia capacity and proliferative ability in DN-CML patients. These results indicate that reversing the immune suppression of PB NK cells by blocking TIGIT while improving the proliferation of BM NK cells via targeting CD57 may be more effective in removing tumor cells.

Hitting More Birds with a Stone: Impact of TGF-β on ILC Activity in Cancer

Transforming growth factor (TGF)-β is a central immunosuppressive cytokine within tumor microenvironment inhibiting the expansion and function of major cellular components of adaptive and innate immune system. Among them, compelling evidence has demonstrated that TGF-β is a key regulator of natural killer (NK) cells, innate lymphoid cells (ILCs) with a critical role in immunosurveillance against different kinds of cancer cells. A TGF-β rich tumor microenvironment blocks NK cell activity at multiple levels. This immunosuppressive factor exerts direct regulatory effects on NK cells including inhibition of cytokine production, alteration of activating/inhibitory receptor expression, and promotion of the conversion into non cytotoxic group I ILC (ILC1). Concomitantly, TGF-β can render tumor cells less susceptible to NK cell-mediated recognition and lysis. Indeed, accumulating evidence suggest that changes in levels of NKG2D ligands, mainly MICA, as well as an increase of immune checkpoint inhibitors (e.g., PD-L1) and other inhibitory ligands on cancer cells significantly contribute to TGF-β-mediated suppression of NK cell activity. Here, we will take into consideration two major mechanisms underlying the negative regulation of ILC function by TGF-β in cancer. First, we will address how TGF-β impacts the balance of signals governing NK cell activity. Second, we will review recent advances on the role of this cytokine in driving ILC plasticity in cancer. Finally, we will discuss how the development of therapeutic approaches blocking TGF-β may reverse the suppression of host immune surveillance and improve anti-tumor NK cell response in the clinic.

Targeting of CXCR3 improves anti-myeloma efficacy of adoptively transferred activated natural killer cells

Background

The peculiar multiple myeloma microenvironment, characterized by up-regulated levels of several inflammatory chemokines, including the CXCR3 receptor ligands CXCL9 and CXCL10, limits NK cell positioning into the bone marrow by interfering with CXCR4 function. It is still unclear if the consequent reduced influx of transferred cells into the tumor represents a potential limiting factor for the success of NK cell-based adoptive therapy. We hypothesize that inhibition of CXCR3 function on NK cells will result in increased tumor clearance, due to higher NK cell bone marrow infiltration.

Methods

Since different activation protocols differently affect expression and function of homing receptors, we analyzed the bone marrow homing properties and anti-tumor efficacy of NK cells stimulated in vitro with two independent protocols. NK cells were purified from wild-type or Cxcr3^−/− mice and incubated with IL-15 alone or with a combination of IL-12, IL-15, IL-18 (IL-12/15/18). Alternatively, CXCR3 function was neutralized in vivo using a specific blocking antibody. NK cell functional behavior and tumor growth were analyzed in bone marrow samples by FACS analysis.

Results

Both activation protocols promoted degranulation and IFN-γ production by donor NK cells infiltrating the bone marrow of tumor-bearing mice, although IL-15 promoted a faster but more transient acquisition of functional capacities. In addition, IL-15-activated cells accumulated more in the bone marrow in a short time but showed lower persistence in vivo. Targeting of CXCR3 increased the bone marrow homing capacity of IL-15 but not IL12/15/18 activated NK cells. This effect correlated with a superior and durable myeloma clearance capacity of transferred cells in vivo.

Conclusions

Our results demonstrate that in vitro activation affects NK cell anti-myeloma activity in vivo by regulating their BM infiltration. Furthermore, we provided direct evidence that CXCR3 restrains NK cell anti-tumor capacity in vivo according to the activation protocol used, and that the effects of NK cell-based adoptive immunotherapy for multiple myeloma can be improved by increasing their bone marrow homing through CXCR3 inhibition.

Bone Marrow NK Cells: Origin, Distinctive Features, and Requirements for Tissue Localization

NK cell maturation is a continuous process, which initiates in the bone marrow and proceeds in peripheral tissues, where NK cells follow distinct differentiation routes. Drastic phenotypic changes are observed during progression from precursors to mature NK cells, including changes of expression and functionalities of several chemoattractant receptors. Upon differentiation, mature NK cells migrate outside the bone marrow; as well, peculiar subsets of NK cells can also home back to or localize in this anatomic compartment to play specific functions. In humans, NK cells with a tissue resident phenotype have been identified in bone marrow, sharing similarities with tissue resident memory CD8+ T cells; while in mouse, long-lived NK cells undergo homeostatic proliferation in this site during viral infections. The mechanisms underlying NK cell subset localization in the bone marrow have only recently started to be investigated, especially in pathological settings such as tumors or infections. In this review, we discuss the phenotype and function of NK cells as well as their requirements for bone marrow maintenance and/or homing.

Differential microRNA expression between decidual and peripheral blood natural killer cells in early pregnancy

STUDY QUESTION

Have decidual natural killer (dNK) cells a different microRNA (miRNA or miR) expression pattern compared to NK cells circulating in the peripheral blood (pb) of healthy pregnant women in the first trimester of gestation?

SUMMARY ANSWER

dNK cells have a unique miRNA profile, showing exclusive expression of a set of miRNAs and significant up- or down-regulation of most of the miRNAs shared with pbNK cells.

WHAT IS KNOWN ALREADY

dNK cells differ from pbNK cells both phenotypically and functionally, and their origin is still debated. Many studies have indicated that miRNAs regulate several important aspects of NK cell biology, such as development, activation and effector functions.

STUDY DESIGN, SIZE, DURATION

Decidua basalis and peripheral blood specimens were collected from women (n = 7) undergoing voluntary termination of gestation in the first trimester of pregnancy. dNK and pbNK cells were then highly purified by cell sorting.

PARTICIPANTS/MATERIALS, SETTING, METHODS

miRNAs expression was analysed by quantitative RT-PCR (qRT-PCR)-based arrays using RNA purified from freshly isolated and highly purified pbNK and dNK cells. Results from arrays were validated by qRT-PCR assays. The bioinformatics tool ingenuity pathway analysis (IPA) was applied to determine the cellular network targeted by validated miRNAs and the correlated biological functions.

MAIN RESULTS AND THE ROLE OF CHANCE

Herein, we identified the most differentially expressed miRNAs in NK cells isolated from peripheral blood and uterine decidua of pregnant women. We found that 36 miRNAs were expressed only in dNK cells and two miRNAs only in pbNK cells. Moreover, 48 miRNAs were commonly expressed by both NK cell preparations although at different levels: 28 were upregulated in dNK cells, while 15 were downregulated compared to pbNK cells. Validation of a selected set (n = 11) of these miRNAs confirmed the differential expression of nine miRNAs: miR-10b and miR-214 expressed only in dNK cells and miR-200a-3p expressed only in pbNK cells; miR-130b-3p, miR-125a-5p, miR-212-3p and miR-454 were upregulated while miR-210-3p and miR-132 were downregulated in dNK cells compared to pbNK cells. IPA network analysis identified a single network connecting all the miRNAs as well as their significant involvement in several classes of functions: 'Organismal injury, Reproductive system disease, Inflammatory disease' and 'Cellular development'. These miRNAs target molecules such as argonaute 2, tumour protein p53, insulin and other genes that belong to the same network and significantly influence cell differentiation and pregnancy.

LIMITATIONS, REASONS FOR CAUTION

In the present study, the cellular network and biological functions modulated by miRNAs differentially expressed in dNK and pbNK cells were identified by IPA considering only molecules and relationships that were with confidence 'experimentally observed' in leucocytes. The decidual and pbNK cells that were analysed here are a heterogeneous population and further study will help to disentangle whether there are differences in miRNA production by the different subsets of NK cells.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study describing a different miRNA expression profile in dNK cells compared to matched pbNK cells during the first trimester of pregnancy. Our findings improved the body of knowledge on dNK cell biology and strongly suggest further investigation into the roles of miRNAs that are differentially expressed in human dNK compared to pbNK cells. Our results suggest that specific miRNAs can modulate dNK cell origin and functions, highlighting a potential role of this miRNA signature in human development and diseases.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from the Istituto Pasteur, Fondazione Cenci Bolognetti, the European NoE EMBIC within FP6 (Contract number LSHN-CT-2004-512040), Istituto Italiano di Tecnologia, and Ministero dell'Istruzione, dell'Università e della Ricerca (Ricerche Universitarie), and from Università Politecnica delle Marche. There are no conflicts of interest to declare.

JAK/STAT signaling in regulation of innate lymphoid cells: The gods before the guardians

Immunity to pathogens is ensured through integration of early responses mediated by innate cells and late effector functions taking place after terminal differentiation of adaptive lymphocytes. In this context, innate lymphoid cells (ILCs) and adaptive T cells represent a clear example of how prototypical effector functions, including polarized expression of cytokines and/or cytotoxic activity, can occur with overlapping modalities but different timing. The ability of ILCs to provide early protection relies on their poised epigenetic state, which determines their propensity to quickly respond to cytokines and to activate specific patterns of signal-dependent transcription factors. Cytokines activating the Janus kinases (JAKs) and members of the signal transducer and activator of transcription (STAT) pathway are key regulators of lymphoid development and sustain the processes underlying T-cell activation and differentiation. The role of the JAK/STAT pathway has been recently extended to several aspects of ILC biology. Here, we discuss how JAK/STAT signals affect ILC development and effector functions in the context of immune responses, highlighting the molecular mechanisms involved in regulation of gene expression as well as the potential of targeting the JAK/STAT pathway in inflammatory pathologies.

Natural Killer Cells as Key Players of Tumor Progression and Angiogenesis: Old and Novel Tools to Divert Their Pro-Tumor Activities into Potent Anti-Tumor Effects

Immune cells, as a consequence of their plasticity, can acquire altered phenotype/functions within the tumor microenvironment (TME). Some of these aberrant functions include attenuation of targeting and killing of tumor cells, tolerogenic/immunosuppressive behavior and acquisition of pro-angiogenic activities. Natural killer (NK) cells are effector lymphocytes involved in tumor immunosurveillance. In solid malignancies, tumor-associated NK cells (TANK cells) in peripheral blood and tumor-infiltrating NK (TINK) cells show altered phenotypes and are characterized by either anergy or reduced cytotoxicity. Here, we aim at discussing how NK cells can support tumor progression and how induction of angiogenesis, due to TME stimuli, can be a relevant part on the NK cell-associated tumor supporting activities. We will review and discuss the contribution of the TME in shaping NK cell response favoring cancer progression. We will focus on TME-derived set of factors such as TGF-β, soluble HLA-G, prostaglandin E₂, adenosine, extracellular vesicles, and miRNAs, which can exhibit a dual function. On one hand, these factors can suppress NK cell-mediated activities but, on the other hand, they can induce a pro-angiogenic polarization in NK cells. Also, we will analyze the impact on cancer progression of the interaction of NK cells with several TME-associated cells, including macrophages, neutrophils, mast cells, cancer-associated fibroblasts, and endothelial cells. Then, we will discuss the most relevant therapeutic approaches aimed at potentiating/restoring NK cell activities against tumors. Finally, supported by the literature revision and our new findings on NK cell pro-angiogenic activities, we uphold NK cells to a key host cellular paradigm in controlling tumor progression and angiogenesis; thus, we should bear in mind NK cells like a TME-associated target for anti-tumor therapeutic approaches.

Translating the anti-myeloma activity of Natural Killer cells into clinical application

Natural Killer cells (NK) are innate effector cells with a critical role in immunosurveillance against different kinds of cancer cells, including Multiple Myeloma (MM). However, the number and/or function of these lymphocytes are strongly reduced during MM progression and in advanced clinical stages. A better understanding of the mechanisms controlling both MM and NK cell biology have greatly contributed to develop novel and combined therapeutic strategies in the treatment of this incurable hematologic malignancy. These include approaches to reverse the immunosuppressive MM microenvironment or potentiate the natural or antibody-dependent cellular cytotoxicity (ADCC) of NK cells. Moreover, chemotherapeutic drugs or specific monoclonal antibodies (mAbs) can render cancer cells more susceptible to NK cell-mediated recognition and lysis; direct enhancement of NK cell function can be obtained by means of immunomodulatory drugs, cytokines and blocking mAbs targeting NK cell inhibitory receptors. Finally, adoptive transfer of ex-vivo expanded and genetically manipulated NK cells is also a promising therapeutic tool for MM. Here, we review current knowledge on complex mechanisms affecting NK cell activity during MM progression. We also discuss recent advances on innovative approaches aimed at boosting the functions of these cytotoxic innate lymphocytes. In particular, we focus our attention on recent preclinical and clinical studies addressing the therapeutic potential of different NK cell-based strategies for the management of MM.